Combine Fresno chiles, garlic, sugar, fish sauce, salt, and 3 tablespoons oil in a blender and process until perfectly smooth. Pour the marinade into a medium bowl and add shrimp, making sure they are well coated. Allow the shrimp to marinate for 10 to 15 minutes.
Heat the remaining 1 tablespoon oil in a large nonstick skillet over medium-high heat. Once the oil starts to shimmer, carefully place the shrimp in the skillet, leaving any excess marinade behind. If necessary, cook in batches to prevent overcrowding the pan. Turn the shrimp once, cooking until they are charred around the edges, about 2 minutes per side. Remove pan from heat.
Arrange the shrimp on a platter. Squeeze fresh lime juice on them, scatter with fresh basil leaves and Thai chilies, for extra heat. Enjoy!
